Many current designs of mattress foundations (commonly referred to as “box springs”) utilize a single layered filler cloth sewn to a border fabric or multilayered bordered panel, together which form a cover that is attached to and covers the top and sides of the foundation frame. Typical practices incorporate an internal layer of cardboard or some form of densified fiber web on top of the foundation frame just below the external filler cloth layer.
The main role of the insulating layer is to provide a durable, abrasion resistant material located between the filler cloth and the frame of the foundation. Foundation frames are typically constructed from wood and/or steel or other metals, and current filler cloths would become worn and would easily tear if positioned directly adjacent to the foundation frame. Insulating layers also provide opacity and cushioning that help obscure the steel wire grid or wooden slats in the foundation frame. Insulating layers are typically attached to the top and/or sides of the foundation frame by stapling to wooden frames or by hog-ringing to the sides of steel wire frames.
The resulting foundation frame with the incorporated insulation layer is then upholstered with a cover comprising a filler cloth sewn to the border panel, thus covering the top and sides of the foundation.
The drawback to using cardboard insulating layers is that their use has a tendency to produce noises in the foundation after limited use. The cardboard layer must also be attached, usually stapled, to a wooden foundation frame in a separate assembly step. This additional assembly operation is also required when using densified fibrous web insulating layers.